1. Field of the Invention
The present invention relates to a color picture tube device having a tension-type shadow grille.
2. Description of the Background Art
FIG. 21 is a partially sectional side view showing a conventional color picture tube device having a tension-type shadow grille. In FIG. 21, 1 denotes a panel forming the envelope of the color picture tube, 2 denotes a funnel forming the envelope of the color picture tube together with the panel 1, 3 denotes a phosphor screen formed by arranging red, blue and green phosphors in order on the inside surface of the panel, 4 denotes an electron gun, 5 denotes electron beam emitted from the electron gun, 6 denotes a deflection yoke for electromagnetically deflecting the electron beam 5, and 7 denotes a tension-type shadow grille serving as a color-selecting electrode.
FIG. 22 shows the structure of the conventionally used tension-type shadow grille 7. In FIG. 22, 8 denotes a frame formed of a steel material such as stainless steel (SUS), for example, and 10 denotes an aperture grille 10 having slit-like apertures 11 and tape-like elongate pieces 9 formed of 0.1-mm-thick rimmed steel, for example. The aperture grille 10 is fixed and held by welding on the frame 8, while being tensed in one direction. The character 10a denotes damper wire and 10b denotes damper spring.
Next, the operation will be described. The inside of the color picture tube is kept at a high vacuum with the envelope formed of the panel 1 and the funnel 2. The electron beam 5 emitted from the electron gun 4 is led to strike the high-voltage-applied phosphor screen 3 on the inside surface of the panel 1 and causes it to emit light. At the same time, the electron beam 5 is deflected from side to side and up and down by the deflecting magnetic field formed by the deflection yoke 6, which forms a picture display area called a raster on the phosphor screen 3. A picture is seen in this picture display area by observing, from the outside of the panel 1, the distribution of the red, blue, and green luminous intensities on the phosphor screen 3 corresponding to the quantity of irradiation of the electron beam 5. An enormous number of slit-like apertures 11 are arranged in order on the shadow grille. The electron beam 5 passes through the apertures 11 to geometrically strike given position on the red, blue, and green phosphor stripes on the phosphor screen 3 for correct color selection. The shadow grille 7 formed of the tape-like elongate pieces 9 is tensed in one direction by the frame 8.
FIG. 23 is a front view of the phosphor screen 3 seen from the viewer side. In FIG. 23, the center of the phosphor screen 3 is shown as the Z-axis in the direction perpendicular to the screen, and the vertical direction is shown at V and the horizontal direction at H. The distances from the center axis Z to an end of the vertical axis V and an end of the horizontal axis H are taken as 1v and 1h, respectively. For the relation between the structure of the shadow grille 7 and the phosphor screen 3, the V direction corresponds to the tape-like elongate pieces 9 and the tape-like elongate pieces 9 are tensed in the vertical direction V.
The recent technical trend in conventional color picture tube devices having such structure is toward flat panels (phosphor screens). Since conventionally used color picture tubes are made of vacuum chambers of glass, flat panels have not been used for weight reduction. On the other hand, recent advancement of the technology, coupled with development in simulation technology, is enabling the use of flatter panels. According to experiments made by the inventors, however, as shown in FIG. 24, when a face of a man is imaged in a close-up in a picture tube having a perfectly flat plane-parallel plate glass as the panel 1, for example, the man's face looks as if it was concave in the center.
The reason for this will be described with the panel 1 formed of a plane-parallel plate glass shown in FIG. 24. In FIG. 24, the upper half (above the Z-axis) shows the section in the vertical axis (V) direction and the lower half (below the Z-axis) shows the section in the horizontal axis (H) direction. In this case, when the viewer 19 sees the phosphor screen 3 on the panel 1 at a point separated by 95 mm from the panel 1, for example, an apparent screen 20 forms as shown by the one-dot chain line in FIG. 25. That is to say, while, in the center of the screen, it is seen at a position raised by about one-third of the thickness T0 of the panel glass, it further warps up by .DELTA.T as it approaches the periphery of the screen. Accordingly, when seen from the viewer 19, the apparent screen 20 is dented in the center as shown by the one-dot chain line. This causes the man's face to be seen as if it was concave in the center.
FIG. 26 shows a conventional example of an improvement for this problem, where, like in FIG. 24, the part above the Z-axis shows the section in the vertical axis (V) direction and the part below the Z-axis shows the section in the horizontal axis (H) direction. This panel 1 is flat in the vertical direction and has a wedge .DELTA. TH in the peripheral part of the screen in the horizontal direction. In this case, the apparent screen 20 forms as shown by the one-dot chain line 20 in FIG. 27. That is to say, in the vertical direction, it is the same as that formed in the conventional flat panel. In the horizontal direction, the apparent screen is made flatter, which is a remarkable improvement as compared with the conventional plane-parallel plate panel 1. However, the insufficient flatness in the horizontal direction and the problem of flatness in the vertical direction still produce an uncomfortable impression.